Attenuator for high frequency pickup devices



June 28, 1949. I JVM. VAN BEUREN 2,474,795

ATTENUATOB FOR HIGH-FREQUENCY PICKUP DEVICES Original Filed Jan. 17, 1944 JNVENTOR (/0701 M. van Bea/"en Patented June 28, 1949 ATTENUATOR FOR, HIGH-FREQUENCY PICKUP DEVICES John M. van Beuren, Morristown, N. J., assignor to Measurements Corporation, Boonton, N. J., a corporation of New Jersey Original application January 17, 1944; SerialNo.

518,645. Divided and this application December 19, 1945, Serial No. 636,035

6 Claims.

invention relates to an attenuator, especially a type of attenuator employed in picking up radio frequency energy from a field.

This application is a division of my co-pending application, Serial No. 518,645, filed January 17, 1944.

One purpose of this invention is to provide an attenuator which can readily be used in making measurements, for example in connection with signal generators, noise meters and the like. However, this invention is equally applicable to devices for attenuation controlin many other types of radio and audio frequency measurement.

Another purpose of this invention is to provide an attenuator in which the pickup circuit and transmission line connecting this pickup circuit with the indicating device are of relatively low impedance and consequently display relatively high efficiency. Actual measurements with this device have shown an increase in efiiciency of from 100to 200 per cent, over devices of types hitherto employed in the art.

Reference is now made to the accompanying drawing, where:

Fig. 1 represents partly in longitudinal section, one embodiment of an attenuator constructed in accordance with the present invention.

Fig. 2 represents, likewise partly in longitudinal section, an alternative form of attenuator according to this invention.

Fig. 3 is an end elevation, taken at the pickup end of the attenuator shown in Fig. 1.

Fig. 4 is an end elevation, taken at the pickup end of the attenuator shown in Fig. 2.

Fig. 5 is an end elevation of a modified form of the attenuator shown in Fig. 1.

Referring now to Fig. 1, there is here shown an outer shielding tube I5. Within tube I5 there is arranged a second metallic tube I6, which is of such diameter, compared with tube I5, as easily to slide therewithin. While tube I6 is illustrated as being in contact with tube I5, such contact is not essential and any suitable mechanical device may be employed to facilitate the sliding of one tube Within the other.

Referring now to both Figs. 1 and 3, there are here shown two conductors 22 and 23 extending, at the active end of tube I6, from points 25 and 26, diametrically opposite upon the periphery of the tube. These conductors are turned longitudinally inward when they approach sufliciently close to one another at a point along the axis of tube I6 and constitute a transmission line 22,

23' of the parallel conductor type. Of course such transmission line may likewise be supplied with any suitable shielding, such as indicated by the tube 24. Any suitable indicating device I3 is connected to the rear ends of the conductors 22' and 23'.

In using the above described form of attenuator, it is preferred that it be so placed that the pickup conductors, 22 and 23, in Fig. 1, shall be transverse to the electro-magnetic field in which the attenuator is placed. However, it may be found possible under some conditions to employ attenuators according to this invention with fields which are not transverse to the pickup conductors.

The action of the pickup conductors 22 and 23 is to form a single low impedance loop by their connection with tube I6. Since tube I6 may be formed of a material having low resistance, and since the effective cross-section of tube I6 may be made comparatively great, it will be seen that the loop thus formed will present low impedance, compared with the conventional type of loop.

As will be apparent to one skilled in the art, the form of attenuator shown in Figs. 1 and 3 is suited especially for connection to a balanced type of indicating or measuring instrument, where both input terminals are balanced with respect to the ground.

For certain applications, the efficiency of the above-described form of attenuator may be increased by using a resistance element as a line termination at the pickup end, such as two resistors in lieu of the end portions, conductors 22 and 23 in Figs. 1 and 3. Such resistors will usually bechosen so as to present a total resistance suitable as a terminating resistance for the surge impedance of the transmission line connected to such resistors.

Fig. 5 shows pickup conductors 22 and 23 made of high resistance material, so as to afford the total desired terminating resistance. In this form, such resistors act simultaneously as terminating resistances and as pickup elements.

While I have described sliding element I6 as a tube, it can be seen that the interior space thereof not occupied by the various conductors and shields performs no useful functions and therefore this space may be filled with the material of which the tube is composed. Under these conditions, there will no longer be any need for the additional shielding tubes enclosing the transmission lines, such as tube 24 in Fig. 1, since element I6 will then act as sufficient shield.

In practice, a solid rod may have a longitudinal hole extending therethrough and corresponding in position and extent to the interior bore of tube 24, for example. In the case of the form of Figs. 1 and 3, the hole would be located along the central axis of such solid rod.

In Figs. 2 and 4 is shown an alternative form of my attenuator, using a solid rod, acting in. the manner just described, The peripheral portion; 31 of rod 40 corresponds to the inner tube I Ev of the form of Figure 1. Pickup conductors 22 and 23 are connected thereto at opposite points 25 and; 26 by any suitable means, such. as. solder. just explained, only that portion or the space he;

1 tween the peripheral portion and the central" portion which is not occupied; conductors; may

be filled in by metal. Therefore. the portion, of the rod between the periphery and the center must allow room for conductors22 and, A3.

At the rear end, rod 40 beprovided: with a. tubular extension 33, shielding the transmission lines, until they enter indicator l3, or a separate shielding member may be employed in lieu of thisextension.

While I have illustrated. my invention thfi descriptionof: certain examples thereof, and; certain applications, such illustrations. are not. ex.- clusive, and the scope of my intention is, only limited by the hereunto. appended: claims, since many modifications andadaptations. will be ap: parent to those skilled in the. art.

I claim:-

1. Electricalattenuator including a plurality of concentric conducting tubes, one sliding closely within the other, two pick-up. conductors extend? ing substantially: wholly radially at. least partly across one end of the inner one of said tubes, each of saidconductors having the. peripherally located extremity thereof electrically connected to a predetermined point upon the periphery of said inner tube, the twopoints thus established being substantially 180-apart, and having the other extremitythereof bent substantially through 90 degrees and extending as a --transmission line longitudinally of said inn-er tube, emerging from the other end of said tube and connected to a measuring device, whereby the active portions of said pickup-conductors do not materially'exceed in length the minimum distance between said transmission line and said' innertube, and do not project a substantial distance beyond the end of said inner tube.

2. Electrical attenuator including two conducting tubes, one-sliding wit-Inn the other, a shielded parallel 2-Wll6 transmission line extending along the common axis of both said; tubes, for connection to a measuring device at the end of said transmission line extending beyond the ends of said tubes, and two pickup conductors, respectively-extending substantially radially, one irorn the other end of each conductor said transmission line to a point upon the periphery of the inner one of said tubes, the points of connection of said respective pickup conductors to said inner tube being located substantially 180 degrees apart.

3; Electrical attenuator including an outer conducting tube and a conducting rod slidable therewithin, said rod having a longitudinal hole extending therethrough, substantially along the axis thereof two transmission conductors extending through said longitudinal hole and bent substantially so as to extend radially at the active endoi; each conductor and being connected to said rod. at; ints substantially apart, the other ends of" both conductors extending beyond the rear of the attenuator so as to be connected to a measuring device, whereby said rod functions as the outer shielding conductor of a shielded transmission line, and whereby such bent over portions of said two conductors function as pickup elements.

ettenuat r ae et 1. n whi th ed a ly tendin por i n. o e ch pickup duc or nclud a er na in si tor Pr pertiqaed t on a t th surge im eda c o r ns i sion ine. onstitu by the lensidinally extending portions of both said con, ct" s,

hsrebrs d r iswri t, at l t a sermon f e ku conductor.

E e rica attenua or n udinean oute meta i tube, a cylindr ca m t ll c bo y lidabls thereWithi-n and having a centrally. located axial ba e thereelqna a twin nduc o t an missiqn exten in t rou h sa d o e. m ns for c nmee the r a ndo s id i t a at n devic and r p ckup eleme ts, located subtan aly a t e m and of a d bod connec respectively to. points 180- apart upon said front end of said body and respectively to the front end oi each conductor: of said line, and projectingbe= rend said front an of a d ody only suffioiently to be insulated from intermediate portions thereof.

6. Electrical attenuator according to claim 5, inwhichsa d p cku e ment a a h. f med of resistive mate el so a to u ction simultane o s y s p ls pe ements a d a ne t rminatin resi t r JOHN M. VAN- BEUREN.

REF R NCE CI E The following references are or record in the file of this patent:

UNZ ED STATE-s ATEN Number Name Date 2 29 ,1 Geers June, 1, 19 2,33 5 2! hinde D 1943 

